But have you seen a visual representation of what these classes match? Probably not. Therefore I created a visualization that illustrates which part of the ASCII set each character class matches. Call it a cheat sheet if you like:

I rarely see these character classes used because they tend to obscure the meaning of regular expressions because support across the standard unix tools and documentation is uneven. For example, GNU grep supports [:blank:] but the man page for GNU grep doesn't mention it. Solaris grep doesn't support character classes at all, unless you're using /usr/xpg4/bin/grep, which may. YMMV with HP-UX, AIX, IRIX/ULTRIX, etc, which all ship with their own custom implementations of regular expressions. GNU Emacs adds [:unibyte:], [:multibyte:], [:word:], [:nonascii:], [:graph:], [:ascii:], and some of those are also defined in the POSIX standard. Python may not support "standard" character classes at all-- I couldn't find any mention of them in the online docs. The actual meaning of these character classes varies as well depending on your locale environment variables. This sometimes is a good thing! Ultimately, unless you have the privilege of controlling where your regular expression is used in all cases, you have to fall back to the minimum supported syntax.